The present invention relates to an internal combustion engine comprising a turbo-supercharger with an automatic bypass.
In the case of volumetric internal combustion engines, such as four stroke and two stroke engines with series-connected piston superchargers, difficulties arise when operating under partial load at high boosting, because the engine suffers from a deficiency of air, and the compressor surges. This problem will become especially acute with high supercharger compression ratios, exceeding about 3.5, which are expected in the future in marine engines having fixed pitch propeller operation. In such an engine there is no way to adapt the engine rotational speed, and thus the compressor rotational speed, to the compressor characteristics by adjusting the propeller pitch.
This deficiency can be overcome in the case of turbo-superchargers in a known manner by means of a bypass, through which the compressor outlet can be connected to the turbine inlet when output is reduced. At higher output it remains closed, except for short duration in special cases, e.g., in the case of hydrofoil boats during displacement travel just before emerging from the water, when because of the high resistance to travel, the engine rotational speed is further reduced.
The action of such a bypass has been known for some time, but in the case of marine engines with fixed pitch propellers, it has, up to the present time, neither been proposed nor used, mainly because of the previous low full load supercharger compression ratios and poor turbo-supercharger efficiencies. In the case of vehicle engines, it has only been used previously in combination with ancillary equipment, such as auxiliary combustion chambers for the turbo-supercharger, auxiliary blowers for the bypass, etc. However, these systems are complicated, so that in practice they are seldom used at the present time.
The before-mentioned high supercharger compression ratio of over 3.5 already exists, particularly in the case of middle-fast four stroke diesel engines, which are increasingly protruding into the output range of large two stroke engines.
In fixed pitch propeller operation, which is characterized by M.about.n.sup.2, or more characteristically where the torque remains partially constant as the rotational speed is reduced, such as in the case of vehicles, constructional machinery, etc., the following three problems occur in the partial output region in volumetric engines having normal supercharger systems without bypass:
(1) When the charge air pressure falls sharply, particularly in the case of constant pressure operation, the engine suffers a deficiency of air, smokes, accelerates badly and the exhaust gas temperature is higher than when under full load.
(2) In order to keep the engine operating line sufficiently far away from the compressor surge limit, the full output point becomes situated in the poor efficiency region, particularly in the case of impulse operation. Then, in the case of rapid fall-off in load, or bypassing or hot water feed to the charge air cooler in order to guarantee spontaneous ignition, the surge limit is nevertheless reached under partial output.
(3) In order for the peak pressure in the cylinder not to become too high, the compressor ratio must, under certain circumstances, be reduced, and this leads to ignition difficulties under small partial loading when starting-up. The known aid method involving preheating of the charge air leads, as stated, to the danger of surging and smoking.
As already stated, in addition to the problematic solution using adjustable turbine and compressor blades, these difficulties can be avoided or at least made less severe by providing between the compressor outlet and turbine inlet an adjustable bypass. However, the known types still always comprise an auxiliary combustion chamber for accelerating the turbo-supercharger independently of the engine, and possibly an auxiliary blower.
These present day known types of supercharger systems incorporating a bypass suffer, among other reasons, from the afore-described complicated construction comprising the auxiliary combustion chamber, auxiliary blower, etc., and this also undermines operational reliability, and the constructional cost becomes considerable. In addition, these systems require additional energy, and this reduces their efficiency.
In most known designs, there is also no possibility of easy adaptation to different engines and operating conditions. Moreover, often costly modification work such as replacing cam plates, etc., is necessary to do this. Furthermore, it is not possible to maintain the throttle member in the bypass temporarily open by external means as is necessary in special cases. Such a case, known as special operation, occurs momentarily when a second slower propeller curve exists, as in the case of hydrofoil boats before emerging from their displacement travel.
Therefore, it is an object of the present invention to provide a turbo-supercharger with an automatically controlled bypass, which is constructionally simpler than known designs, and which substantially obviates their drawbacks.
Another object is to enable required operational behavior to be easily set.
A further object is to make use of the rapid pressure and impulse operation.
An additional object is to enable the bypass, if required, to act as a non-return valve.
A further object of the present invention is to minimize leakages which have been heretofore unavoidable in the usual piston-controlled valves.
Another object is to enable the non-return valve to act simultaneously as a throttle member for simplification reasons.